1. Field of the Invention
This invention relates to an electrostatic actuator.
2. Description of the Related Art
An electrostatic generator has been well known in the past as an apparatus for converting mechanical energy to electric field energy, and an electrostatic motor is an apparatus for effecting the reverse operation to the above, that is, for converting electric field energy to mechanical energy.
The history of such an electrostatic motor is long, and this motor was already examined from the 18th century. The history of this motor is described in detail in, for example, "Electrostatic Handbook", edited by the Society of Electrostatic Engineering, published by Ohm-sha, pp. 664-675.
The reference described above illustrates an induction motor which utilizes the delay of polarization of dielectrics.
The principle of this induction motor utilizes the time delay of polarization of a dielectric member on the basis of the concept that when the dielectric member is placed inside an electric field, it causes polarization.
In other words, when the dielectric member as a rotor is placed inside a rotating electric field inside a stator, an induction load of the dielectric member has a deviated angle from the rotating electric field due to the time delay.
The interaction between the charge and the rotating electric field results in the turning force.
Motors that use a resistance body in place of the dielectric member are also known. The motors of this kind utilize the phenomenon that the charge induced into the resistance body inside the rotating electric field gets delayed in the direction of the electric field. However, the conventional electrostatic motors involve the following drawbacks.
(1) A force whose direction crosses orthogonally a desired force of operation, that is, the attraction, acts between the resistance body and an electrode. Therefore, a film structure of the motor is difficult to attain.
(2) The motor comprises a rotary mechanism including a stator and a rotor and having a certain gap. A mechanism such as a bearing is used to retain this gap. It is therefore difficult to reduce the gap over a wide area. To accomplish this object, the stator and the rotor must be sufficiently thick so as to improve rigidity. Therefore, the mass of the members for keeping this rigidity becomes great and a density of force (the force that can be generated per unit area) deteriorates.
Accordingly, the motor cannot be made compact in size and its density of force is low, too.
Report No. 737 of the 89th National Meeting of the Society of Electric Engineering, entitled "Electrostatic Actuator Using Resistance Body for Moving Element", proposes an electrostatic actuator capable of solving the problems described above.
This electrostatic actuator comprises a stator having a plurality of belt-like electrodes which are insulated from one another, a moving member which includes an insulator layer and a high resistance body layer and on the surface of which a charge pattern is induced in accordance with a voltage pattern applied to the belt-like electrodes, and control means for driving the moving member by switching the voltage to the belt-like electrodes.
This electrostatic actuator can generate an electrostatic force between solid surfaces and can obtain a greater density of force by reducing the gap between the solid surfaces and increasing its surface area.
Since repulsion is once allowed to act in a direction in which the moving member floats up from the stator, the resultant force can be effectively converted to a driving force.
However, the conventional electrostatic actuator is not free from the problem that the structure is complicated, because the moving member has a two-layered structure of the insulator layer and the high resistance body layer.
Since the resistance body is utilized, the time constant for charging the moving member must be set to a sufficiently long time in comparison with the time necessary for the moving member to move the distance required for moving in each cycle at the time of driving the belt-like electrodes. In other words, there is the problem that an initial charging time is long at the start of operation.
It is an object of the present invention to provide an electrostatic actuator whose structure can be simplified and can reduce the charging time in view of the conventional problems described above.